Proton conduction is one of the most important known natural phenomena. For example, a variety of chemical processes, including redox reactions and acid/base catalysis, are coupled to proton transfer. In addition, numerous biomolecules, such as electrochemically-driven proton pumps in mitochondria and voltage-gated proton channels in phagocytes, have evolved specific structural motifs that facilitate proton translocation. Moreover, the function of an increasingly diverse array of technologically-relevant devices, including fuel cells, electrolyzers, batteries, sensors, and transistors, crucially relies upon proton transport. Indeed, given the ubiquity of proton conduction in chemistry, biology, and materials science, it is hardly surprising that this area has captured the attention of scientists for over two hundred years.
Due to the fundamental and technological importance of proton conduction, solid-state proton-conducting materials, such as ceramic oxides, solid acids, sulfonated polymers, porous solids, and metal-organic frameworks, remain the focus of much research effort. Within this context, naturally occurring proteins have received relatively little attention, which is quite surprising given the prevalence of proton translocation in biology. Moreover, relative to their artificial counterparts, protein-based materials possess notable advantages that include intrinsic biocompatibility, structural modularity, tunable physical properties, ease and specificity of functionalization, and generalized expression/purification protocols. Thus, naturally occurring proteins constitute a promising class of proton conductors, whose potential remains largely unrealized.
From an applications perspective, protein-based proton conducting materials are uniquely positioned to enable the next generation of bioelectronics. For example, given the importance of protons (and ions in general) for electrical signaling in biology, protonic transistors represent a natural choice for interfacing rugged traditional electronics and decidedly more fragile biological systems. Indeed, one can envision the direct and robust transduction of biochemical events into electrical signals with such devices. However, despite this potential for biological applications, there have been very few literature examples of protonic transistors, including a notable recent report of maleic chitosan-based devices from Rolandi and coworkers. Within this context, protonic transistors from naturally occurring materials represent an untapped source of novel materials for various solid-state, bioelectronics, and other devices.
The inventors of the present disclosure have developed a new class of devices based on materials from certain cephalopod structural proteins. Cephalopods are members of the class Cephalopoda and include cuttlefish, squid, and octopus. It has been shown previously that certain proteins from Cephalopods contain a large number of charged amino acid residues, consisting of one to six highly conserved repeating subdomains separated by variable linker regions, and possess little to no secondary/tertiary structure. Some such proteins are also remarkably robust, even when exposed to acidic conditions, heated to 80° C., or processed via standard lithographic protocols. Moreover, within cephalopod skin cells (iridophores), these proteins form platelets, which play a crucial role in cephalopod structural coloration as part of modular Bragg reflector-like structures.
Herein, the inventors of the present invention provide the art with materials derived from such proteins, which such materials have large protonic conductivity and which may be utilized in transistors, proton-permeable membranes, protonic wires, and myriad other structures.